C++Talk.NET

Patrick Kowalzick · Guest

Dear all,

sorry, I always forget this thing:

Is this foo:

int foo(int i)
{
++i;
return i-1;
}

the same like this foo:

int foo(int i)
{
return i++;
}

? As I am alway scared using the ++ operators in compact forms, I'd better
ask......

Thanks,
Patrick

****************************

Reply form:

[ ] both foos are identical in the functionality and well defined
[ ] keep your fingers away from "return i++"
[ ] keep your fingers away from "return ++i"
[ ] do not know

Please mark the correct answers. More than one answer might be correct.

Victor Bazarov · Guest

Patrick Kowalzick wrote:

Patrick Kowalzick · Guest

Dear Victor,

JKop · Guest

int Blah()
{
int k = 5;

return ++k;
}

The above function returns 6.

--

The below function returns 5.

int Blah()
{
int k = 5;

return k++;
}

--

When you put ++ before the name: The object is incremented. The value of the
expression is the object's value *after* the increment.

When you putt ++ after the name: The value of the expression is the object's
value *before* the increment. The object is incremented.

Maybe the following will enlighten?:

class Number
{
private:

unsigned k;

public:

Number& operator++()
{
//This gets called when you do ++object
//Note that it returns by reference

k += 1;

return *this;
}

Number operator++(int)
{
//This gets called when you do object++
//Note that it returns by value

//First we create a temporary, making a copy of the current object
Number temp = *this;

//Now we proceed with the increment
k += 1;

//But... we return the old value, ie. before the increment
return temp;
}
};

-JKop

JKop · Guest

Patrick Kowalzick · Guest

Dear JKop,

thanks a lot for your explanations. Sorry that I did not express me right,
but I know the thing about post- and pre-increment.

The only problem I have, is to remember in which cases I run into undefined
behaviour. So I'd better ask before Wink

. The compilers are not a good
indicator here, because some may work, and others not (undefined).

I was only *quite* sure that my code is fine, but not 100%.

Thanks,
Patrick

Karl Heinz Buchegger · Guest

Patrick Kowalzick wrote:

Ron Natalie · Guest

JKop wrote:

Victor Bazarov · Guest

Karl Heinz Buchegger wrote:

Andrey Tarasevich · Guest

Karl Heinz Buchegger wrote:

Patrick Kowalzick · Guest

Dear Victor, dear Karl Heinz,

Patrick Kowalzick · Guest

Dear Ron,

Andrey Tarasevich · Guest

Victor Bazarov wrote:

Victor Bazarov · Guest

Andrey Tarasevich wrote:

Howard · Guest

"Patrick Kowalzick" <kowalzick (AT) gmx (DOT) net> wrote